Matlab Utilities 1

Antennas and Microwaves

Matlab RFutilities

These Matlab m-files were originally written to display measured or calculated input impedances. The collection of routines allows data to be plotted as Smith Chart, Admittance Chart, Return Loss, VSWR and Mismatch Loss. Frequency markers can be added to each of the plot types.

Over time the routines have been added to so that measured/calculated impedance can be modified before display. A simple transmission line model allows measured data to be de-embedded (using a –ve length). Matching can be achieved using lumped L,C,R elements or transmission lines.

There are CITI file loaders for the HP standard data format and a time domain reflectometry function (actually chirp-Z transform) to display impedance as a function of distance.

The routines that deal with input impedance use the form Zin=A+jB Ohms, rather than the reflection coefficient S11,S22 etc. This is simply because I feel it is easier and more intuitive to work with input impedance in this form.

An additional set of routines to display the transmission parameters : Insertion Loss, Phase Delay and Group Delay use the usual S-parameter form S21,S12 etc. Again because I feel it is easier to work with transmission parameters in this form.

There are routines to convert between S11 and Zin there is a function to convert standard S-param to mixed mode S-param, allowing differential and common mode impedances to be displayed.

The latest addition to the routines allow the design and analysis of stepped and tapered line impedance transformers. These include Chebyschev and Binomial stepped transformers; Exponential , Triangular and Klopfenstein tapered line transformers. There are also routines for realising the designs as Microstrip layouts and exporting them from Matlab to AutoCad DXF format. Finally, there is also a routine for designing broadband Wilkinson splitters.

All m-files have help-comments and there are numerous example scripts. The files are split between 3 folders ‘RFutils’ ,‘RFutils_S’ and Rfutils_M. The zipped files can be downloaded from here. Download Rfutils .

Ideally these should be copied into the Matlab toolbox directory so the search paths become : C:\ Matlab\toolbox\Rfutils , C:\ Matlab\toolbox\Rfutils_S etc.. This is so that the example files that load test data have the correct pathname. Examples that use pathnames are identified in contents.m in Rfutils.

Once you have copied the files and added them to Matlab’s search paths, type :

help rfutils - lists all the functions in Rfutils and Rfutils_S

example1 - run example1

example2 - run example2 etc...through to 11

help rfutils_m - lists all the functions and examples in Rfutils_M

The Smith Chart as displayed using RFutils.

Matlab RFutils

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